A brake system is an apparatus configured to decelerate and stop a driving vehicle while maintaining a stopped state of the vehicle, and includes a parking brake configured to decelerate and stop the driving vehicle while maintaining the vehicle in the stopped state.
The parking brake pulls a parking cable by an operation of a lever provided in one side of a driver seat in the vehicle and then provides a braking force to wheels of the vehicle connected to the parking cable to maintain a state in which the wheels of the vehicle are stopped, and on the other hand, when the lever is released and thus the parking cable is released, the braking force applied to the wheels of the vehicle is removed.
Since the lever has to be operated by a driver when starting to park or drive, which makes the parking brake operable only by will of the driver, using the parking brake has been inconvenient. Accordingly, an EPB (electric parking brake) system in which the parking brake is automatically operated according to an operation state of the vehicle was developed.
The EPB system automatically operates or releases the parking brake and secures braking stability in an emergency by connection with a manual operation mode of the driver according to a switch operation, a HECU (electro-hydraulic control unit), an ECU (engine electric control unit), a TCU (traction control unit), and the like.
The EPB system integrally includes an ECU, a motor, a gear, a parking cable, a braking force sensor (force sensor), and the like. Here, the ECU operates a parking brake actuator after receiving related information from the HECU, the ECU, the TCU and the like through a CAN (controller area network), and then identifying intentions of the driver.
When a motor of the parking brake actuator is operated, since a gear assembly is operated by driving of the motor and then a driving shaft is rotated and the parking cable is pulled by an operation of the gear assembly, the braking force is applied to the wheels of the vehicle, and thus the vehicle maintains a stable state. Here, the gear assembly may include a worm connected to the rotary shaft of the motor so that power is transmittable, and a worm wheel.
The worm and the worm wheel are advantageous for gaining high torque at a large deceleration ratio. However, the motor has to be operated to rotate the worm and the worm wheel, and currents are consumed to operate the motor. Since an environment in which the vehicle has more electrical components and receives a driving force through the motor sharply has been increasing, a structure in which a rotating force of the motor can be transmitted to the driving shaft to which the parking cable is connected with low power consumption and high efficiency, is urgently necessary.
Further, the parking brake actuator receives an operation of the motor through a spur gear, and the spur gear is connected to a worm gear to be driven.
However, since the conventional spur gear and worm gear are connected to each other by insertion-injection molding, and have a structure in which the spur gear is supported using an additional bracket, costs and processes increase.
Further, the conventional parking brake actuator has a structure in which a molding type upper housing formed of a resin material and a worm gear formed of a resin material come into contact with each other, and thus is vulnerable to abrasion.